This invention relates to microelectronic packaging and more specifically to multilayer ceramic packaging technology for microelectronic components.
The microelectronics industry is constantly striving for further miniaturization of components to increase speed and functionality for a given system. This has led to the development of the so-called very large scale integration (VLSI) of a number of electronic components such as integrated circuit chips, discrete components such as inductors, capacitors, resistors, wave guides and fiber optic coupling devices into a single integrated package. The large number of interconnections between the components mounted within the package have driven the creation of socalled Multilayer Ceramic technology (MLC), as described in Microelectronics Packaging Handbook, Van Nostrand Reinhold publishers, New York 1989, pages 455-522 which provides for a thermally efficient, multi-component carrier capable of three-dimensional interconnect circuitry.
In general, fabricating MLC carriers utilizes particles of high temperature withstanding dielectric material such as alumina and glass suspended in an organic binder and formed and dried into so-called xe2x80x9cgreen sheetsxe2x80x9d. Individual sheets of tape are printed with metalization and other circuit patterns, stacked on each other, laminated together at a predetermined temperature and pressure, and then fired at an elevated temperature routine upon which the majority of the binder material vaporizes off while the remaining material fuses or sinters. Where alumina glass is generally used as the insulating material, tungsten, molybdenum or molymanganese is typically used for metalization, and the part is fired at temperatures of about 1,600 degrees C in a reducing atmosphere such as hydrogen. This is known as high temperature co-fired ceramic (HTCC) technology. In a typical HTCC process, screen-printed resistors can be used and only high-melting point refractory metal paste are used as conductors.
The undesirable high processing temperature and requisite hydrogen atmosphere and, more importantly, the limited electrical performance of the high melting point refractory metals has led to the development of low temperature co-fired ceramic (LTCC) technology. Low temperature ceramic tape is commercially available from DuPont Company as a GREEN TAPE brand ceramic tape which sinters at approximately 850 degrees C and exhibits thermal expansion similar to alumina. The low temperature processing permits the use of air-fired resistors and precious metal thick film conductors such as gold, silver or their alloys.
However, due to the large amount of heat generated by the active circuit components and during the fabrication process, thermal management of these packages is a driving concern. Unfortunately, high temperature brazing is unavailable to the LTCC modules.
A discussion of thick film technology, and high and low temperature co-fired ceramic tape technology is found in xe2x80x9cDevelopment of a Low Temperature Co-fired Multilayer Ceramic Technologyxe2x80x9d, by William Vitriol et al., ISHM Proceedings 1983, pages 593-598.
In general, HTCC-type packaging is most commonly used for applications requiring high material strength, high thermal conductivity and compatibility for high temperature brazing for mounting lead frames, heat sinks, wave guides and other mounting hardware, and where high conductivity traces are not required. LTCC packaging on the other hand, with its high conductivity silver or gold metalization is commonly used for applications which must route sensitive, typically low-power, high frequency signals, or which require a large number of interconnecting traces. Those designing systems requiring the advantages of both types of carriers would therefore be required to make bulkier separate packages.
The principal and secondary objects of this invention are to provide a single integrated ceramic package or module which displays the advantages of both high temperature and low temperature cofired ceramic multilayer packages. It is a further object of this invention to provide a mechanism for bonding and interconnecting a plurality of ceramic carriers.
These and other valuable objects are achieved by providing a interconnecting bonding layer comprising both electrically conductive and non-conductive structures for interfacing electrical contact points or pads on the interfacing surfaces of two or more ceramic packages including LTCC and HTCC types. Further, the layer may comprise enhanced thermal conductivity regions for interfacing heat sources with heat dissipating structures. Further, the layer may have apertures to allow passage of prominent structures from one carrier into corresponding cavities in another carrier.